The present invention relates to an adjustable steering apparatus. More particularly, the invention relates to an adjustable steering apparatus which utilizes a tooth-to-tooth meshing engagement for fixing or releasing a steering jacket including a steering wheel.
A tiltable, telescopic steering apparatus has been known which permits a steering wheel in front of a driver to be tilted upward or downward for tilt adjustment and to be axially extended or retracted for adjustment in order that the driver may drive in an optimum position.
Such a steering apparatus generally has a constitution wherein the steering jacket (jacket tube) rotatably supporting a column shaft having the steering wheel mounted to its distal end is fixed to a movable bracket vertically movable as clamped by an upper clamp (stationary bracket) fixed to a vehicle body. An operation lever is fixed to a nut in threaded engagement with a clamp bolt penetrating through these brackets. The operation lever is turned thereby operating a cam mechanism for causing the stationary bracket to clamp the movable bracket. A frictional force occurring between these brackets is used to fix the steering jacket to place.
By the way the following problem exists in the case where the frictional force between the stationary bracket and the movable bracket is used to fix the movable bracket to place, thereby to fix the steering jacket to place. If a greater force than the frictional force is applied to the steering jacket, the steering jacket slidably moves within the stationary bracket forwardly or upwardly, so that the steering wheel is shifted from an initial set position. For instance, if the driver hits against an air bag at collision so that an excessive input is applied to the steering jacket via the air bag, the fixation position of the steering jacket is displaced. As a result, the air bag may be deployed in an improper position. The air bag may not work sufficiently effectively unless the driver hits against the air bag squarely. If the driver hitting against the air bag displaces the steering jacket from its fixation position so that the air bag is shifted forwardly or upwardly relative to the vehicle body, the air bag may not be able to exhibit its performance fully.
In this connection, a steering apparatus has been proposed which adopts a fixing method based on the tooth-to-tooth meshing engagement in place of the fixing method based on the frictional force.
As shown in FIG. 8 and FIG. 9, for example, Japanese Unexamined Patent Publication No. 99640/1996 discloses a tiltable, telescopic steering column wherein an operation lever (not shown) is axially movably fitted with a clamp bolt 110 penetrating through an elongated hole 108 for tilting formed in an upper clamp 101 and through an elongated hole 109 for telescoping formed in a distance bracket 103. A tilt-lock tooth portion 114 is formed on an edge of the elongated hole 108 for tilting, whereas a telescopic-lock tooth portion 115 is formed on an edge of the elongated hole 109 for telescoping. A first movable member 118 having a lock tooth portion 116 meshingly engageable with the tilt-lock tooth portion 114 and a second movable member 121 having a lock tooth portion 119 meshingly engageable with the telescopic-lock tooth portion 115 are assembled to the clamp bolt 110 in such a manner that the movable members may be pressed against the upper clamp 101 and the distance bracket 103, respectively. The clamp bolt 110 penetrates through bolt-through holes 117, 120 formed in the first movable member 118 and the second movable member 121. The first movable member 118 is formed with a vertical groove 122 for engagement with the second movable member 121.
The steering column disclosed in Japanese Unexamined Patent Publication No. 99640/1996 operates as follows. When the operation lever is turned to clamp the distance bracket 103 by means of the upper clamp 101, the lock tooth portion 116 of the first movable member 118 is meshed with the tilt-lock tooth portion 114 so as to inhibit the vertical movement of the clamp bolt 110. In the meantime, the lock tooth portion 119 of the second movable member 121 is meshed with the telescopic-lock tooth portion 115 so as to inhibit the distance bracket 103 from moving forwardly or rearwardly relative to the vehicle body. As a result, the steering wheel is prevented from shifting from the set position in spite of the excessive input overcoming the clamping force of the clamp bolt 110.
According to the steering column of the above patent publication, however, the first movable member 118 for tilting and the second movable member 121 for telescoping are adapted to move in unison so that the meshing relations between the respective tooth portions of the movable members and individually corresponding tooth portions affect each other. This dictates the need to set high dimensional accuracies of the finished tooth portions. With low dimensional accuracies, the tooth portions are in poor meshing engagement, failing to achieve a positively fixed condition. That is, such high dimensional accuracies as to simultaneously establish the meshing engagements between the lock tooth portion 116 of the first movable member 118 and the tilt-lock tooth portion 114 and between the lock tooth portion 119 of the second movable member 121 and the telescopic-lock tooth portion 115 are required, which results in difficult manufacture process and assembly process.